The invention relates to a method of manufacturing a semiconductor device comprising a semiconductor body having a surface which is provided with a coil having a magnetic core, in which method, the surface of the semiconductor body is provided with a first metallization layer having a first pattern of conductor tracks embedded in insulating material, and a surface, which faces away from the semiconductor body, on which a layer of a magnetic material is deposited in which the magnetic core is formed by means of an etch treatment, whereafter the magnetic core and the adjacent surface of the first metallization layer are provided with a second metallization layer having a second pattern of conductor tracks embedded in an insulating material, said second pattern of conductor tracks being connected to the first pattern of conductor tracks so as to form windings of the coil.
This method can particularly suitably be used to manufacture integrated circuits comprising one or more coils. Such integrated circuits are used, for example, in mobile telephone apparatus. In the manufacture of integrated circuits, the semiconductor body is provided with semiconductor elements which are electrically interconnected. The surface of the semiconductor body is provided with a number of metallization layers with patterns of conductor tracks embedded in an insulating material. By adding only a few more process steps, coils can be incorporated, as indicated hereinabove, in integrated circuits.
The coil is provided with a magnetic core. As a result, a coil is obtained having a self-induction which may be a factor of the order of the relative magnetic susceptibility xcexcr larger than the self-induction of an equally large coil without a core. By virtue thereof, a coil whose self-induction is as large as possible can be realized on a part of the semiconductor body surface which is as small as possible.
In U.S. Pat. No. 3,614,554, a description is given of a method of the type mentioned in the opening paragraph, in which the first metallization layer is formed by successively applying a layer of an insulating material to the surface of the semiconductor body, forming the first pattern of conductor tracks on this layer and covering this pattern and the layer of insulating material situated next to this pattern with a further layer of an insulating material. The core is formed by etching in a layer of permalloy (an alloy of nickel, iron; cobalt, magnesium and copper) having a thickness of approximately 750 nm. The coil covers a surface area of approximately 3 by 2.5 mm.
In practice it has been found that the known method is not very suitable for the manufacture of coils for circuits which are intended for processing signals whose frequencies are above 100 MHz. At these high frequencies, coils manufactured by means of the known method exhibit self-inductions which do not exceed those of coils which do not have a core of magnetic material.
It is an object of the invention to provide a method by means of which it is possible to produce coils whose self-induction is much greater than that of equally large coils without a core of magnetic material.
To achieve this, the method mentioned in the opening paragraph is characterized in that the first metallization layer is formed on the surface of the semiconductor body in such a manner that the surface of said metallization layer facing away from the semiconductor body is flat, whereafter the layer of a magnetic material is deposited in a thickness below 50 nm.
In accordance with the invention, the thickness of the core of the coil is chosen so as to be much smaller than the thickness of 750 nm mentioned in the known method. As a result, the coil is smaller in section, so that the self-induction should be proportionally smaller. It has however been found that, at these high frequencies, a thin layer has a relative magnetic susceptibility xcexcr which is so much higher than a thicker layer that the coil formed nevertheless has a higher self-induction. If the thickness of the core is chosen to be, for example, a factor of 10 smaller, then the sectional dimension of the coil is also reduced by approximately a factor of 10, however, since the relative magnetic susceptibility of the core may be a factor of 500 higher, a coil is formed having a self-induction which nevertheless may be a factor of 50 higher.
If in the known method use is made of such a much thinner magnetic layer, the coils formed still do not have a higher self-induction than coils without a core. In the method in accordance with the invention, in which the layer of magnetic material is deposited on a flat surface, the coils formed do have a higher self-induction. In the known method, the layer of magnetic material is deposited on a surface which is not flat. An approximately 500 nm thick layer of an insulating material is applied to the approximately 750 nm thick conductor tracks of the first pattern of conductor tracks. The topography of this layer corresponds to that of the conductor tracks. If the very thin layer of magnetic material is deposited on such a non-flat surface, then the layer formed is not homogeneous. Said layer exhibits differences in thickness and, possibly, interruptions which may be the reason why the magnetic core does not lead to he desired high self-induction of the coils. If the layer of magnetic material is deposited on a flat surface, then the desired homogeneous layer is obtained and coils having the desired high self-inductions are formed.
A substantial freedom of choice of the material to be used for the layer of magnetic material is obtained if the conductor tracks of both patterns of conductor tracks are embedded in an insulating material in such a manner that the magnetic core is electrically insulated from the conductor tracks of both patterns. The magnetic material may be an alloy of electroconductive materials, such as iron, chronium, tantalum, cobalt, niobium and zirconium, for example an alloy of iron and 4.6 at. % chromium, 0.2 at. % tantalum and 7.4 at. % nitrogen. Preferably, the layer of magnetic material is a layer packet composed of magnetic sub-layers having a thickness below 10 nm which are separated from each other by intermediate layers of a non-magnetic material, such as copper or an insulating material, having a thickness below 5 nm. In this manner, a magnetic core can be formed having a xcexcr which is very high at frequencies above 100 MHz. If, for example, approximately 6 nm thick sub-layers are formed of a magnetic alloy comprising, apart from iron, cobalt, niobium and zirconium, which sub-layers are separated from each other by approximately 2 nm thick intermediate layers of aluminium nitride, then such a packet has a xcexcr of approximately 400 at 100 MHz, a xcexcr of 200 at 1 GHz and a xcexcr of 100 at 400 GHz.
A very compact coil is obtained if the magnetic core is formed in a layer of a magnetic material which is electrically insulating, and the conductor tracks of both patterns of conductor tracks are embedded in insulating material in such a manner that the magnetic core electrically contacts the conductor tracks of both patterns. An example of such a material is manganese-zinc-ferrite (Mn0.50Zn0.42Fe2.03O4) which has a resistivity of 106 xcexcxcexa9cm and which is substantially insulating in comparison with metals, such as aluminium which has a resistivity of 2.7 xcexcxcexa9cm.
To ensure that the conductor tracks of the first pattern of conductor tracks are electrically insulated from the magnetic core, the first metallization layer may be obtained by successively applying a layer of an insulating material onto the surface of the semiconductor body, forming the first pattern of conductor tracks on this layer, covering this pattern and the layer of insulating material next to this pattern with a further layer of an insulating material, and planarizing this further layer of insulating material. This planarization may be carried out by means of a customary chemico-mechanical polishing treatment or by applying a layer of a photoresist followed by an etch treatment in a plasma or etch bath in which the photoresist and the insulating material are etched at an equal rate. As a result, a layer of an insulating material remains on the conductor tracks. In practice, this remaining layer does not have a uniform thickness. In addition, this layer must be relatively thick to ensure that the underlying conductor tracks are not locally exposed during the planarization treatment.
Preferably, the first metallization layer is formed by successively applying a layer of an insulating material to the surface of the semiconductor body, forming grooves in this layer, depositing a metal layer on the layer of insulating material and into the grooves, subjecting the metal layer to a planarization treatment until the insulating layer is exposed again, and depositing a further layer of an insulating material. In this case, the further layer of an insulating material, which can be very homogeneously deposited in a customary manner, also has a flat surface and may be thinner than, for example, 100 nm. This thin layer of insulating material causes the conductor tracks and the magnetic core to be insulated from each other.
This preferred embodiment of the method in accordance with the invention has the additional advantage that there is a great freedom of choice of the metal to be used for the conductor tracks. For example, the conductor tracks in this embodiment may be made of copper, so that the coil exhibits a small electric resistance. The planarization treatment can be carried out in a customary manner.
The number of materials that can be chosen for the part of the coil windings formed by the second metallization layer is also greater if the second metallization layer is formed by successively covering the core and the adjacent part of the first metallization layer with a further layer of an insulating material, forming grooves in this layer without exposing the magnetic core, depositing a layer of metal on the further layer of insulating material and into the grooves, and subsequently subjecting the metal layer to a planarization treatment until the insulating layer is exposed again. The accuracy with which the grooves are formed can be so high that the conductor tracks of the second pattern can be insulated from the magnetic core by a layer of an insulating material of a very small thickness below 100 nm.
The conductor tracks of the first pattern of conductor tracks are embedded, in a simple manner, in insulating material such that the magnetic core electrically contacts the conductor tracks of the first pattern if a layer of an insulating material is provided on the surface of the semiconductor body; this is achieved by successively forming grooves in this layer, depositing a layer of a metal on the layer of insulating material and into the grooves, subjecting the metal layer to a planarization treatment until the insulating layer is exposed again. If the layer of insulating magnetic material is subsequently deposited, then this layer directly contacts the conductors of the first pattern of conductors.
The conductor tracks of the second pattern of conductor tracks are embedded, in a simple manner, in insulating material such that the magnetic core electrically contacts the conductor tracks of the second pattern if a further layer of an insulating material is provided on the core and the adjoining part of the first metallization layer; this is achieved by successively forming grooves in this layer, thereby exposing the core, depositing a layer of metal on the further layer of insulating material and into the grooves, and subjecting the metal layer to a planarization treatment until the insulating layer is exposed again.
As indicated hereinabove, this method makes it possible to choose the metal used for both patterns of conductors from a wide range of metals, and for example copper may be used.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter, which constitute(s) a non-limitative example.